The present invention relates to a method of growing dwarf plants in which plant propagative material, such as a young plant, a seed, a bulb, a rooted cutting, a sucker or the like, is placed in a plant pot with a substrate whose volume is insufficient for full growth of said plant material and whose wall permits gas exchange. The invention furthermore relates to a plant pot made of a material permitting gas exchange such as fired clay.
It is a known practice to grow plants such a cactuses in pots with a greatly reduced size of frequently as little as 50 cc or even less. Such miniature cactuses then have a very slow rate of growth because of the extremely small volume in the pot so that it is possible to culture a large number of dwarf cactuses in a small space. However, there is one problem in this respect inasfar as once they have filled the pot, the roots develop as a spirally coiled cluster or tangle adjacent to the inner face of the pot wall. Such a root coil is detrimental because the roots then hardly put out any root hairs for the uptake of nutrients and sooner or later the plant will fail to flourish. To get around this difficulty it is then necessary to transfer the plant into a larger pot so that the roots will then have sufficient space and nutrient substrate and for some time at least the roots will cease to grow in a coiled form and will grow outwards into the additional nutrient medium.
However, after such repotting the plant will then grow at its normal rate because the roots now have a sufficient quantity of nutrient substrate; and after a certain growth stage of the roots, they will again start to develop in coils and further repotting will be required. As time goes on the plant will need larger and larger pots, if it is to do well, with a steady increase in size. For this reason it is only possible to delay the growth of plants, as for example cactuses, by putting them in miniature pots; true, permanent dwarf culture of the plant is not possible with this known method.
The German unexamined specification, 2,434,538 has an account of a method of growing plants such that coiling of the roots may be effectively prevented for a certain length of time if the pot is lined with a layer of open-celled soft foam with a thickness of about 1 to 10 mm.
When the roots have grown as far as this soft foam layer they firstly stop growing without forming coils and the plant puts out new, active roots in the middle of the mass of roots. It is said that in this case the stems and leaves of the plant grow very quickly and there are very small distances between the buds and the plant blooms 25 to 30 days earlier than normally would be the case in conventional pots. That is to say, the plant will be of a smaller size than in conventional pots as may be seen from FIG. 2 of the said specification as compared with FIG. 1. However, a true dwarf habit is not possible and is furthermore not intended.
On the other hand true permanent dwarf growth may be produced by the bonsai method originating in Asia. Here as well very small plant pots are used for growing the plants and at the same time the nutrient supply to the plant is very restricted. To prevent natural coiling of the roots against the pot wall regular trimming of the mass of roots is called for so that a considerable amount of time is necessary in this method of plant culture.
Lastly the Austrian Pat. No. 350,831 describes a method for limiting the amount of growth of plants involving culture in very small containers in which root coiling is prevented by having apertures in the wall of the container which are so small that they substantially prevent the growth of the roots therethrough but however allow the passage of nutrients. The container, whose wall thickness is preferably at the most four times the clearance width of the apertures, then has to be surrounded by nutrient substrate, the plant then taking up at least a part of the nutrients as needed for growth to the desired size by way of small root hairs from the surrounding nutrient substrate, whereas the porous plant container has to be of a size that is smaller than that which would be needed for growth to the desired size.
However, this method suffers from the drawback that the coiling of the roots is only effectively prevented as long as the apertures, which have a size of about 0.1 to 0.3 mm, do not become clogged. Therefore a continuous check has to be kept on the container. Furthermore the material has to meet stringent conditions as there would otherwise be a danger of the container bursting owing to the pressure of root growth with a consequent loss in the growth limiting effect. Such containers are therefore to be manufactured of non-corroding material and are preferably made of stainless steel gauze with a wall thickness of about 0.1 mm. Such materials are costly and may be hard to obtain.